1. Field of the Invention
The invention relates to clutches and, more particularly, relates to friction clutches having self-adjusting mechanisms for compensating for wear of the friction discs.
2. Discussion of Related Art
Clutches such as over-center power take off (PTO) clutches are well known to those skilled in the art and selectively transfer torque from a drive member such as a drive ring or a flywheel to a driven output shaft. The typical clutch includes a hub fixed to the shaft, a pack of friction discs connected to the drive member, a splined clutch face plate which is slidably mounted on the hub, and an adjusting ring which is threadedly mounted on the hub. The clutch is engaged under the operation of a suitable linkage assembly which typically comprises a yoke which is slidably mounted on the output shaft, a manually operated lever which slides the yoke on the shaft, and at least one over-center lever arm assembly. Each lever arm assembly comprises an over-center lever arm and a pivot link which are disposed between the yoke and the face plate and which are operable, upon sliding movement of the yoke toward the face plate, to drive the face plate toward the drive member, thereby compressing the friction discs and engaging the clutch. The lever arm of each over-center lever arm assembly also engages the drive ring so that the drive ring serves as a pivot point for the lever arm. The point at which the maximum forward stroke of the face plate terminates is thus dependent upon the position of the adjusting ring.
Normal use of a clutch results in wear of the friction discs and related components and eventually results in decreased capacity requiring replacement of the friction discs. The life of the clutch can be extended by compensating for clutch wear by threadedly mounting the adjusting ring on the hub so that, by rotating the adjusting ring on the hub and moving the adjusting ring axially towards the face plate, the pivot point for the over-center lever assembly is moved towards the clutch pack, thereby advancing the point at which the maximum forward stroke of the face plate terminates towards the disc stack and compensating for disc wear. Such adjustment has traditionally been performed manually when the operator detects a decrease in clutch engaging effort or a decrease in transmitted torque. Such manual adjustment is labor intensive, particularly since it typically requires at least partial disassembly of the clutch assembly to provide access to the adjusting ring. Such adjustment may also be postponed or neglected by some operators until after wear exceeds tolerances.
Various slack adjusting devices have been proposed to automatically adjust a clutch to compensate for clutch wear, thus obviating the need for manual adjustment. Such devices typically comprise relatively complex worm wheel driven configurations which are relatively expensive to manufacture and assemble, which cannot be used on stock clutches, and which have proven somewhat unreliable in use. Such automatic slack adjusters also typically do not have a direct bearing on clutch operation and thus cannot be used to control the maximum torque transmitting capacity of the clutch. Examples of such prior art self-adjusting clutch mechanisms can be found in U.S. Pat. No. 4,189,043 to Steinhagen, U.S. Pat. No. 4,445,600 to Schmidt, and U.S. Pat. No. 5,090,536 to Asada.